Hypothesis

Telomere attrition velocity, corrected for proliferation rate, serves as a quantitative readout of epigenetic entropy generated by mismatch repair deficiency and oxidative stress in histologically normal colon epithelium distant from tumors.

Mechanistic Rationale

Recent work shows that biological age acceleration raises colorectal polyp risk by 16% per year[1] and that ~15% of cancers exhibit deficient mismatch repair, producing thousands of mutations per replication cycle[2]. Field cancerization extends reduced DNA repair protein expression up to 10 cm from tumor margins[3], creating zones where repair errors accumulate without a proportional increase in cell division. Telomere dysfunction appears early in the adenoma‑to‑carcinoma transition, with 55% of small adenomas showing chromosomal instability[4].

If telomeres functioned merely as division counters, their shortening rate would scale strictly with mitotic count. However, telomeric chromatin is sensitive to transcriptional stress and DNA damage signaling; TERRA (telomeric repeat‑containing RNA) levels rise in response to oxidative lesions and recombination intermediates. Mismatch repair failure elevates basal oxidative stress and generates persistent single‑stranded gaps that can invade telomeric repeats, accelerating repeat loss independent of S‑phase passage. Moreover, epigenetic drift—measured as increased Shannon entropy of CpG methylation across promoter‑associated islands—correlates with global transcriptional noise and has been linked to mitochondrial retrograde signaling that influences telomere maintenance.

Thus, telomere length may integrate two orthogonal information streams: replication history and epigenetic/repair entropy. The normalized attrition rate (ΔTL / divisions) could therefore reflect cumulative informational disorder rather than mere mitotic count.

Testable Predictions

1. In microdissected crypts from normal‑appearing mucosa at 0 cm, 2 cm, 5 cm, and 10 cm from tumor edges, the ratio of telomere shortening rate (measured by STELA or qPCR) to Ki‑67‑positive fraction will increase with distance from the tumor in a manner that correlates with methylation entropy (calculated from bisulfite‑sequencing of a CpG‑shore panel).
2. Organoid cultures derived from mismatch‑repair‑deficient (MLH1‑silenced) colon epithelium will exhibit a higher ΔTL/division ratio than isogenic proficient controls when proliferation is matched by thymidine supplementation, even in the absence of exogenous genotoxic stress.
3. Pharmacological reduction of epigenetic noise (e.g., using low‑dose DNMT inhibitors to restore methylation fidelity) will decrease the ΔTL/division ratio in dMMR organoids without altering division rate.

Experimental Approach

• Obtain paired tumor‑adjacent normal colon specimens from patients undergoing resection for sporadic CRC (n ≥ 30). Laser‑capture microdissect crypts at defined distances from the tumor margin.
• Quantify telomere length per sample using single‑telomere length analysis (STELA) to capture distribution shifts; parallel Ki‑67 immunostaining provides division index.
• Perform targeted bisulfite sequencing of 500 CpG shores across the genome; compute Shannon entropy per crypt as a measure of methylation disorder.
• Stratify samples by MMR status (immunohistochemistry for MLH1/MSH2/MSH6/PMS2) and test whether the ΔTL/division ratio predicts methylation entropy better than raw telomere length or division count alone (multiple regression analysis).
• Validate causality in CRISPR‑engineered colonic organoids: induce MLH1 knockout, match proliferation via CDK4/6 inhibitor titration, measure telomere dynamics and methylation entropy over 30 population doublings.

Falsification would occur if ΔTL/division ratio shows no correlation with methylation entropy across spatial gradients or genetic backgrounds, or if manipulating epigenetic entropy fails to alter telomere attrition when proliferation is held constant.